NA mostly sucks at worlds because...

Almost every team plays for winning regular season. They care more about winning record than learning from their failures and pushing past their mistakes to grow from them. They'd rather use the same strat(s) that they know they can get by with in NA but that fail vs better opponents on the world stage. They don't think enough for themselves, trust THEIR playstyles and play to their strengths while shoring up their weaknesses, and copy-paste strats champs and builds from "superior" regions.

Think about it. Have you ever watched Naruto and Shippuden? Ok, so think of NA top teams as Kakashi. He copies other Jutsu's much like NA copies Korea or China. And vs mid or high level (at least high level in Naruto) shinobi he gets away with it and looks pretty badass. But then comes Tobito (4th shinobi war) and Madara and Kaguya. Against these guys he has nothing. Because he's always just stolen others jutsu's and tried to outplay them with it by combo'ing in his own at the right times. Well against these opponents he can neither perfectly (if at all) copy them, he can't execute them the same way they can, and he can't outsmart them with the simple tricks he used on other opponents. So he's screwed. This is the typical NA team at worlds.

Now look at Naruto. He gets his butt kicked most of the time. But even when he does, he knows his goal/dream and always works towards it refusing to give up or to be persuaded otherwise by those around him who might think him incapable or advise him to play it safe. He learns from his failures and uses them to grow and improve. He adds other's tricks and jutsu's to his arsenal when possible - putting his own spin on them, and stays true to his strengths. The only team in NA that seems to follow this kind of approach is C9. And despite having to (maybe embarassingly) go through play-ins and barely sneak into worlds, they end up going further than any other team from NA the past few years. Coincidence? No. It's difference in mentality, goals, and focus.

Here's hoping a few other teams will take note of that and start putting the lesson into practice this season.